The present invention relates to a vertical internal combustion engine having a crankshaft directed substantially in a vertical direction, particularly a vertical internal combustion engine for an outboard motor.
In a 4-stroke cycle vertical internal combustion engine disclosed in Japanese Laid-Open Patent Publication No. Hei 7-149290, a flywheel is provided on a lower end of a crankshaft directed in a vertical direction integrally and a lubricating oil pump is disposed above the flywheel. Further, at a position above the flywheel, a drive gear is provided on the crankshaft integrally and a speed increasing mechanism is interposed between the drive gear and the lubricating oil pump so that the lubricating oil pump is rotationally driven at a higher speed than that of the crankshaft.
In a 4-stroke cycle vertical internal combustion engine disclosed in Japanese Laid-Open Patent Publication No. Hei 8-100616, a lubricating oil pump is directly connected to a lower end of a cam shaft directed vertically.
According to the engine disclosed in the above-mentioned Japanese Publication No. Hei 7-149290, since the lubricating oil pump rotates at a higher speed than the crankshaft, even if the lubricating oil pump is small-sized, a high discharge ability is obtainable, however, owing to the lubricating oil pump positioning below a bearing portion of the internal combustion engine for pivotally supporting the crankshaft, a part of the crankshaft extending downward from the bearing portion becomes long so that it is difficult to support the flywheel having a large inertial mass stably from a viewpoint of vibration.
According to the engine disclosed in the above-mentioned Japanese Publication No. Hei 8-100616, since no lubricating oil pump is disposed above the flywheel, the flywheel can be arranged near the internal combustion engine and as the result the flywheel having large inertial mass can be supported stably. However, since rotational speed of the cam shaft is a half of that of the crankshaft, there are inconveniences that the discharge ability is low and the lubricating oil pump becomes large necessarily.
Some vertical internal combustion engines for outboard motors in which balancer shafts are used for reducing vibration are disclosed in Japanese Laid-Open Patent Publications Nos. Sho 63-192693, Hei 3-224894 and Hei 4-337143.
The Japanese Publication 63-192693 and 3-224894 disclose balancer mechanisms for offsetting and reducing the primary vibration in an in-line 2-cylinder 4-stroke cycle internal combustion engine.
On the one hand, the Japanese Publication 4-337143 discloses a balancer mechanism in a 4-stroke cycle in-line 4-cylinder engine which aims at reducing the secondary vibration because the engine has an advantage that the primary vibration does not occur fundamentally. However, as secondary vibration becomes larger, the balancer becomes large-sized more and it becomes necessary to care about balancer shaft supporting constructions and lubricating passages.
The Japanese Laid-Open Patent Publication No. Hei 3-33416 discloses a water-cooled 4-stroke cycle internal combustion engine for propelling ships in which a suction system is arranged on one side and an exhaust system and a cartridge type oil filter are arranged on another side. As shown in FIG. 8 of the above publication, lubricating oil having passed through the oil filter is supplied to a cam shaft pivot portion through some oil passages to lubricate the cam shaft pivot portion.
In a water-cooled 4-stroke cycle internal combustion engine for propelling ships disclosed by the Japanese Laid-Open Patent Publication No. Hei-8-100616 too, a lubricating oil passage connected between an oil filter disposed near a suction system on a front face of a crankcase and a valve moving system is arranged on the side of an exhaust system.
However, in the internal combustion engine of the publication 3-33416, an electric parts box as well as the oil filter cartridge is disposed on the side of the exhaust system and therefore if the electric parts box becomes large for meeting demands to electric control system, it is difficult to dispose the oil filter cartridge at the same position.
In the internal combustion engine of the publication 8-100616, the oil filter is disposed on a front face of the crankcase and maintenance work is easy. But since an oil passage for lubricating oil after passing through the oil filter is provided in a exhaust system, the oil passage is long to increase flow resistance, capacity of the oil pump has to be improved and amount of oil is necessarily increased.